1. Field of the Invention
The present invention relates generally to combustion gas turbine engines and, more particularly, to combustion gas turbine engines that employ catalytic combustion principles in the environment of a lean premix burner. Specifically, the invention relates to graded metal catalytic tube that can be used in conjunction with a lean premix burner of a combustion gas turbine engine to reduce the production of undesirable nitrogen oxides.
2. Description of the Related Art
As is known in the relevant art, combustion gas turbine engines typically include a compressor section, a combustor section, and a turbine section. Large quantities of air or other gases are compressed in the compressor section and are delivered to the combustor section. The pressurized air in the combustor section is then mixed with fuel and combusted. The combustion gases flow out of the combustor section and into the turbine section where the combustion gases power a turbine and thereafter exit the engine. In its simplest form, the turbine section includes a shaft that drives the compressor section, and the energy of the combustion gases is greater than that required to run the compressor section. As such, the excess energy is taken directly from the turbine/compressor shaft or may be employed in the form of thrust, depending upon the specific application and the nature of the engine.
As is further known in the relevant art, some combustion gas turbine engines employ a lean premix burner that mixes excess quantities of air with the fuel to result in an extremely lean burn mixture. Such a lean burn mixture, when combusted, beneficially results in reduced production of nitrogen oxides (NOX), which is desirable in order to comply with applicable emissions regulations, as well as for other reasons.
The combustion of such lean mixtures can, however, be somewhat unstable and thus catalytic combustion principles have been applied to such lean combustion systems to stabilize the combustion process. Catalytic combustion techniques typically involve flowing a mixture of fuel and air over a catalytic material that may be in the form of a precious metal such as platinum, palladium, rhodium, iridium, and the like. When the air/fuel mixture physically contacts the catalyst, the air/fuel mixture spontaneously begins to combust. Such combustion raises the temperature of the air/fuel mixture, which in turn enhances the stability of the combustion process.
In previous catalytic combustion systems, the catalytic materials typically were applied to the outer surface of a ceramic substrate to form a catalytic body. The catalytic body was then mounted within the combustor section of the combustion gas turbine engine. Ceramic materials were often selected for the substrate inasmuch as the operating temperature of a combustor section typically can reach 1600xc2x0 Kelvin (1327xc2x0 C.; 2420xc2x0 F.), and ceramics were seen as the best substrate for use in such a hostile environment based on considerations of cost, effectiveness, and other considerations. In some instances, the ceramic substrate was in the form of a ceramic washcoat applied to an underlying metal substrate, with the catalytic material being applied to the ceramic washcoat.
The use of such ceramic substrates for the application of catalytic materials thereto has not, however, been without limitation. When exposed to typical process temperatures within the combustor section, the ceramic washcoat has been subject to spalling and/or cracking due to poor adhesion of the ceramic washcoat to the underlying metal substrate and/or mismatch in the coefficients of thermal expansion of the two materials. Such failure of the ceramic washcoat subsequently reduces catalytic performance. The catalytic material additionally can be lost directly from the ceramic material due to poor adhesion of the catalytic material onto the ceramic washcoat as well as mismatch in the coefficients of thermal expansion of the two materials. It is thus desired to provide an improved catalytic body that substantially reduces or eliminates the potential for reduced catalytic performance due to the use of ceramic materials.
In certain lean premix burner systems, it may be desirable to achieve the ultimate lean mixture by adding air in multiple stages to the fuel during the combustion process. With such a system, the operating parameters such as the temperature of the combustion process can be tightly controlled to beneficially reduce the production of undesirable emissions therefrom. It is thus desired that an improved catalytic body be provided that can be used in conjunction with such a multi-stage combustor section.
In view of the foregoing, an improved metal catalytic tube includes an elongated metal member formed at least partially of metal particles and including a catalytic enhancement incorporated into the metal member. The metal member is formed with a cavity and includes an inner surface defined by the cavity and an outer surface opposite the inner surface. The metal member has a porosity at the outer surface that is greater than the porosity at the inner surface. The porosity at the inner surface is sufficiently low that the metal member can carry a quantity of gas through the cavity without the gas leaking through the inner surface of the metal member.
The metal member can be constructed in various fashions, and typically is formed out of a quantity of metal particles that are compressed and bonded together. The metal particles can be in the form of metal fibers, metal powder, metal wire, and metal mesh, as well as other forms. The variation in porosity between the inner surface and outer surface can be achieved by using metal particles of different sizes, by varying the compression of the particles from the inner surface to the outer surface, by applying metal particles to the exterior surface of a solid metal pipe, as well as by other methods.
The catalytic enhancement likewise can be in many forms. For instance, the catalytic enhancement can be in the form of discrete particles of catalytic material that are combined with the metal particles to make the metal member. Alternatively, the metal particles themselves can be coated with catalytic material. Still alternatively, the catalytic enhancement can be in the form of a coating of catalytic material on the outer surface of the metal member, and can additionally include a ceramic coating such as a washcoat interposed between the catalytic materials and the metal particles of the metal member.
An objective of the present invention is thus to provide a metal catalytic tube that is formed at least partially out of metal particles.
Another objective of the present invention is to provide a metal catalytic tube having a catalytic enhancement incorporated therein.
Another objective of the present invention is to provide a metal catalytic tube formed with a cavity that can carry a quantity of gas through the cavity substantially without leakage.
Another objective of the present invention is to provide a metal catalytic tube having a metal member formed with a cavity and having an inner surface and an outer surface, the porosity of the metal member being greater at the outer surface then at the inner surface.
Another objective of the present invention is to provide a combustion gas turbine engine having a compressor section, a combustor section, and a turbine section, the combustor section including a metal catalytic tube that reduces undesirable emissions from the combustion gas turbine engine.
Another objective of the present invention is to provide a combustion gas turbine gas engine employing a metal catalytic tube in a multi-stage combustor section of the engine.
In view of the foregoing, an aspect of the present invention is to provide a metal catalytic tube, the general nature of which can be stated as including an elongated metal member formed with a cavity, the metal member being formed at least partially of metal particles. The metal member has an inner surface defined by the cavity and an opposite outer surface, with the metal member having a porosity at the outer surface that is greater than the porosity at the inner surface. The metal member is structured to carry a quantity of gas through the cavity substantially free of leakage through the inner surface, and includes a catalytic enhancement incorporated into the metal member.
Another aspect of the present invention is to provide a combustion gas turbine engine, the general nature of which can be stated as including a compressor section a combustor section, and a turbine section, with the combustor section including a metal catalytic tube. The metal catalytic tube includes an elongated metal member and a catalytic enhancement incorporated into the metal member. The metal member is formed with a cavity and is formed at least partially of metal particles. The metal member has an inner surface defined by the cavity and an opposite outer surface, with the metal member having a porosity at the outer surface that is greater than the porosity at the inner surface. The metal member is structured to carry a quantity of gas through the cavity substantially free of leakage through the inner surface.
Still another aspect of the present invention is to provide a method of combusting a quantity of fuel with a quantity of gas, the general nature of which can be stated as including the steps of flowing the fuel in a longitudinal direction over the outer surface of an elongated metal catalytic tube, interacting the fuel with a catalyst integrated with the metal catalytic tube to ignite the fuel, flowing the gas through a cavity in the metal catalytic tube, and mixing the gas with the ignited fuel.